A wheel loader as a self-propelled working vehicle is configured to obtain the driving force for a carrier and the driving force for a working machine from a single engine. Specifically, the driving force for a carrier of the wheel loader is obtained by a so-called HST hydraulic traveling device, or is obtained through a torque converter. Also, a hydraulic cylinder for driving a front working machine is driven by a hydraulic pump that is driven by the engine.
In addition, generally speaking, the wheel loader is often used for simultaneously performing works such as traveling and loading. Therefore, it is important how the output of the engine should be distributed to the carrier's side and the working machine's side in a balanced manner.
In addition, it is important in the wheel loader to balance the traction force (i.e., the driving force for driving a traveling section) and the lift force for elevating the lift arm. For example, the traction force works as the anti-lift force when a work is performed that the wheel loader travels forward and loads sediment into a bucket and then the bucket is lifted by driving a lift arm. In other words, the traction force works in a direction that the lift force of the lift arm is brought back.
Therefore, as the traction force increases, the lift force is reduced. Accordingly, it becomes difficult to perform a work. In response to this, a work is performed with the conventional working vehicle, while the lift force is prevented from being reduced by regulating the traction force by the operator's accelerator manipulation.
On the other hand, too much lift force result in insufficient traction force, and a so-called thrusting performance of thrusting the bucket into sediment gets worse. Accordingly, the lift arm is elevated before sediment and the like into are loaded into the bucket, and thus workability gets worse.
In response to this, as described in the Japanese Patent Application Publication No. JP-A-H05-106243, a working vehicle is proposed that the engine speed is configured to be reduced until the work velocity of a front working machine reaches a predetermined value under the condition that the vehicle velocity is approximately zero and the driving pressure of a front working machine hydraulic cylinder is greater than or equal to a predetermined value. In the working vehicle described in the publication, the traveling torque is reduced when the large driving force for the front working machine is needed. Accordingly, it is possible to increase the lift force by the amount corresponding to the amount of the reduced traveling toque.